Wireless networks aim to provide reliable connectivity for user and high end-to-end throughput performance. Routing is one of the most important factors affecting connectivity and throughput in wireless networks, especially in multi-hop wireless mesh networks. Routing establishment depends on metric values associated with each routing path. The metric typically considers many comprehensive factors, such as hop count, delay time, and link quality. For a wireless network, the hop count and the delay time are relatively easy to measure. On the other hand, the link quality is complicated and difficult to measure, because wireless link environment often is influenced heavily by reliability and interference.
One conventional way of estimating wireless link quality uses the measured packet delivery ratio to represent the link quality of a particular wireless link. To support link quality measuring, unicast probing packets are usually used to probe link's packet delivery ratio.
However, link quality estimation based on the packet delivery ratio cannot reflect how busy the link environment is. Since the physical layer has built-in mechanisms to avoid transmission conflicts, the packet deliver ratio may be quite high, even though the link environment is very poor.
Moreover, the conventional way of estimating wireless link quality does not consider the influence of transmission rate on the link quality. For example, assuming that at the beginning of data transmission, payload packets are transmitted at a high transmission rate. Subsequently, the link environment deteriorates. Accordingly, the transmission rate is adjusted to a lower transmission rate. On the other hand, the packet delivery ratio at a low transmission rate may be higher than at the packet delivery ratio at a high transmission rate. As a result, when the link environment becomes worse, the estimation of link quality using conventional way can actually get better instead of reflecting the worsened link environment. Under these circumstances, the conventional assessment of wireless link quality cannot accurately measure the actual wireless link quality.